The present invention is directed to a multi-layer papermaking fabric which is constructed to retain its rigidity, its uniform knuckle configuration and its uniform drainage characteristics while in use.
Multi-layer forming fabrics are well known and have long been used in the papermaking industry. Preferred structures of such forming fabrics are illustrated in U.S. Pat. Nos. 5,164,249; 4,640,741; and 5,169,709. These patents show various weave structures commonly used to form multi-layered papermaking fabrics. These fabrics possess the above referred desirably characteristics when formed. When put in service on a papermaking machine, the stacked weft yarns which extend transversely of the machine direction of the papermaking machine, have a tendency to become unstacked. This is particularly true when the weft is woven with long floats on the paper support surface and the running surface as in the referred to patents. When the stacked weft yarns become unstacked, the outer yarns slide to one side or the other of the supporting yarns. This movement alters the knuckle pattern presented on the support surface into a random arrangement. The knuckles then mark the paper product being formed on the forming fabric in a non-uniform manner. Further, when the weft yarns shift to the side of the supporting yarns, they fill or alter drainage channels. This results in uneven and sometimes insufficient drainage which results in the production of an inferior paper product.
Multi-layer forming fabrics, having stacked weft yarns, may be woven in higher densities with shorter floats. While this more compact structure presents a more stable fabric, it is very limited in amount of drainage which can be accommodated. Also, shorter weft floats reduce the life of the forming fabric due to greater exposure of the load bearing warp yarns.
Accordingly, it is an object of this invention to provide a multi-layer papermaking fabric in which weft yarns are retained in their woven position when the fabric is in use.
Another object of the invention is to provide a multi-layer papermaking fabric which allows uniform drainage in use.
Another object of the invention is to provide a multi-layered papermaking fabric in which the knuckle pattern on the support surface remains uniform in use.
Another object of the invention is to provide a multi-layer paper forming fabric having the above characteristics.